Neutral-Point Voltage-Balancing Strategies of NPC-Inverter Fed Dual Three-Phase AC Motors

In this article, the mechanism of neutral-point potential oscillations of neutral-point-clamped (NPC) three-level inverter fed dual three-phase ac motors is described. In a dual three-phase ac motor drive system, the three-level NPC inverter can be controlled as one six-phase system or two separate conventional three-phase systems. Therefore, this article extends the traditional control strategy, which injects the uniform zero-sequence voltage into the three-phase system to the six-phase system. The relationship of the uniform zero-sequence voltage and the neutral current is analyzed in detail. Meanwhile, the neutral-point potential-balancing strategy adopting dual zero-sequence voltages is presented in this article. The simulation and experiment verify that the proposed strategy adopting dual zero-sequence voltages has better control of the neutral point potential than the strategy adopting uniform zero-sequence voltage.

Automated summary

This article describes the mechanism of neutral-point potential oscillations in a dual three-phase ac motor system using NPC three-level inverter. It extends the traditional control strategy to the six-phase system and proposes a neutral-point potential-balancing strategy using dual zero-sequence voltages. Simulation and experiment results confirm that the proposed strategy outperforms the traditional strategy in controlling the neutral point potential.